reflections on code, making, and tech

RGB LED

Basic Info

The first thing to know about RGB LEDs (or sometimes just RGBs) is to know that RGB stands for red, green and blue.

There are an infinite number of colors of light you can create with the RGB.

Inside the RGB are three light-emitting diodes, one red, one green, and one blue. Each lead connects to each of these diodes.

Even though there are only three colors, there are four leads. The fourth extra lead is called the common lead. It’s the longest one. The common lead is shared amongst all three diodes and is either the cathode or the anode.

You can think of the RGB as three separate LEDs mushed into one, each has it’s own lead, plus they all share a common one.

The the single lead on the outside directly next to the common lead is the red lead. The one on the opposite side is the blue lead, and the one in the middle next to the common lead is green.

There are two types of RGB LEDs, determined by whether the common lead is an anode or cathode: the common cathode and the common anode.

Common anode (CA) RGB LED: the common lead is the anode, and should be connected to the power. All of the other three leads for the colors are cathodes, and should be connected to ground.

Common cathode (CC) RGB LED: the longest lead is the cathode and should be connected to ground. The other leads for the colors must be connected to power. It’s the opposite configuration of the common anode RGB.

Hooking it Up

Note that you don’t need all the legs of the RGB hooked up for it to work. If you just wire the red lead, you’ll get a red LED. If you wire the green and blue leads, you’ll get a blue-green light.

Know what type of RGB you’re working with.

Two ways to vary the apparent color of the RGB LED include using resistors to make the one color brighter than another, or using pulse width modulation generated by a microcontroller, computer, or an IC like the 555 timer.

In many cases (especially when precise control of the colors is desired), it’s best to use common cathode RGB LEDs. This eliminates the need for transistors.

Connect the common lead to power or ground, depending on the type of RBG you’re using. Then connect your color leads to ground or power respectively. Don’t forget your current-limiting resistors! RGBs will burn out just like regular LEDs if you’re not careful.